A fast-moving storm turned skies from day to night across a wide swath of the Chicago area Thursday, damaging homes and businesses and bringing planes and trains to a halt. And as workers and residents worked to clean up from the storm, the area was bracing for another.

A roof collapsed at the dock area of an industrial building in the suburbs, injuring 40 people, authorities said. West Chicago Police Department spokesman Mike Uplegger said seven people were sent to hospitals and the rest refused treatment at the scene. None of the injuries was considered life threatening.

A large piece of metal scaffolding at Northwestern Memorial Hospital's Prentice Women's Hospital collapsed during the storm, and two people suffered minor injuries but refused treatment, Chicago Fire Department spokesman Larry Langford said. Also, the rear wall of a four-story building under construction on Chicago's North Side collapsed, but no injuries were reported, he said.

Matt Steinkraus, 29, of St. John, Ind. — in Chicago for his wedding on Saturday — was walking downtown with his fiancee and friends when the storm struck.

"As soon as it hit, we made a break for the nearest bar," he said. "We got drenched ... then we went into the bathroom, wrung out our shirts, ran them under the dryer."

More than 185,000 ComEd customers were without power from northern Chicago north to the state line, spokesman Tom Stevens said.

"But looking at the radar, there's another line of storms coming up, so that number could change," Stevens said. "We're doing everything we can right now to get those crews out as quickly as we can."

The severe weather — which included reports of funnel clouds in several western suburbs — felled trees and traffic lights and forced the halt of commuter rail lines throughout the Chicago area. All flights were grounded at O'Hare International Airport and Midway Airport during the storm. They resumed about 40 minutes later, but aviation officials warned passengers to expect delays and cancellations.

Judy Pardonnet, a spokeswoman with Metra commuter rail system said there were delays throughout the system because of debris on the tracks and malfunctioning signals.

"It's going to be a slow commute home for us," she said.

Langford said trees in several areas of the city hit power lines and exploded transformers, setting utility poles on fire.

"This is not a storm that's isolated," Langford said. "This one hit the entire city north to south."

The National Weather Service would not be able to confirm tornado touchdowns until Friday, meteorologist Gino Izzi said. He said 74 mph wind gusts were recorded in Midlothian and near Wrigley Field.

But the weather service was keeping a wary eye on storms and thunderstorms developing to the west in Iowa, fearing they would cause flash flooding as they moved into Illinois. Northern Illinois remained under a flash flood watch, and some areas could see 3-5 inches of rain — of particular concern because the ground is so saturated with water from recent rains, Izzi said.

"If that happens, you could be talking very serious flooding," Izzi said.

In Fox Lake in far-northern Illinois, the Fox River flooded some homes while other residents stacked sandbags to protect their houses, said Ami McEwan, assistant administrator for Lake County.

"Most of them are sandbagging and keeping it at bay," she said.

In downtown Gurnee, just west of Waukegan, workers were stacking sandbags to protect an elementary school from the Des Plaines River, she said. School hadn't yet started for the fall, so no students were affected.

A foot of water stood over roads in the Rochelle area, about 20 miles west of De Kalb, and the Des Plaines River was more than 3 feet above flood stage north of Waukegan, according to the weather service.

Minor to serious flooding also was reported along the northern stretches of the Fox and Rock rivers.

Storms also knocked down trees and damaged buildings north and west of Peoria in central Illinois, adding to the rising water in several rivers. Volunteers and emergency workers were stacking sandbags to protect buildings and homes from the rising Des Plaines and Fox Rivers near Waukegan.

An afternoon storm that included high winds uprooted trees and damaged at least one home in Galesburg, about 40 miles northwest of Peoria, according to the National Weather Service. The storm also blew the windows out of a church in nearby Toulon, and knocked out power lines across Stark County, just north of Peoria.